What is the optimal pH range for removing particulate matter when using alum as a coagulant?

• A. 5.5 to 6.0
• B. 6.0 to 6.5
• C. 6.5 to 7.2
• D. 7.2 to 8.0

Answer: (C)

The optimal pH range for removing particulate matter when using alum as a coagulant is between 6.5 and 7.2. This pH range is important because it facilitates the effective ionization of alum in water, promoting the coagulation process.

When alum is added to water, it dissociates and forms aluminum hydrolysis products, which are essential for agglomerating small particles into larger flocs that can then be removed through sedimentation or filtration. At lower pH values, the solubility of aluminum increases, which can lead to ineffective coagulation and reduced removal of particulate matter. Conversely, at pH values significantly higher than 7.2, the effectiveness of alum may decrease due to the instability of the aluminum species.

Optimal coagulation processes not only improve the efficiency of removing turbidity and particulate matter but also help in maintaining appropriate water quality standards. Meeting these pH conditions ensures that the coagulation process is maximized, leading to more effective water treatment.